U.S. patent application number 14/573899 was filed with the patent office on 2016-06-23 for system and method for automated machining of toothed members.
The applicant listed for this patent is PRATT & WHITNEY CANADA CORP.. Invention is credited to Mario BLAIS, Yan COUSINEAU, William FERRY.
Application Number | 20160175955 14/573899 |
Document ID | / |
Family ID | 56119837 |
Filed Date | 2016-06-23 |
United States Patent
Application |
20160175955 |
Kind Code |
A1 |
FERRY; William ; et
al. |
June 23, 2016 |
SYSTEM AND METHOD FOR AUTOMATED MACHINING OF TOOTHED MEMBERS
Abstract
A system and method for machining a workpiece to provide a
toothed member having a desired tooth pattern. A cutting tool
machines the workpiece to a first depth, thereby forming a
semi-finished tooth pattern, the first depth less than a full depth
to which the workpiece is to be machined to provide the desired
tooth pattern. Dimensions of the semi-finished tooth pattern are
acquired and compared to nominal dimensions. If the acquired
dimensions are not within a tolerance of the nominal dimensions,
the geometry of the cutting tool is modified for correcting
deviations of the acquired dimensions from tolerance and the
workpiece further machined by the modified cutting tool. Once the
dimensions of the semi-finished tooth pattern are within tolerance,
the workpiece is machined to the full depth for providing the
desired tooth pattern.
Inventors: |
FERRY; William;
(Saint-Lambert, CA) ; BLAIS; Mario; (Varennes,
CA) ; COUSINEAU; Yan; (Saint-Amable, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PRATT & WHITNEY CANADA CORP. |
Longueuil |
|
CA |
|
|
Family ID: |
56119837 |
Appl. No.: |
14/573899 |
Filed: |
December 17, 2014 |
Current U.S.
Class: |
700/110 |
Current CPC
Class: |
B23F 23/1225 20130101;
G05B 19/182 20130101; G05B 2219/35035 20130101; Y02P 90/265
20151101; Y02P 90/02 20151101 |
International
Class: |
B23F 23/12 20060101
B23F023/12; G05B 19/18 20060101 G05B019/18 |
Claims
1. A computer-implemented method for machining from a workpiece a
toothed member having a desired tooth pattern, the workpiece
machined using a cutting tool of a numerically controlled machine,
the method comprising: causing the cutting tool to machine the
workpiece to a first depth to provide a semi-finished tooth
pattern, the semi-finished tooth pattern created according to a
geometry of the cutting tool, the first depth less than a full
depth of the desired tooth pattern; acquiring dimensions of the
semi-finished tooth pattern; comparing the acquired dimensions to
nominal dimensions of the semi-finished tooth pattern and
determining whether the acquired dimensions are within a
predetermined tolerance of the nominal dimensions; if the acquired
dimensions are not within the predetermined tolerance of the
nominal dimensions, causing the geometry of the cutting tool to be
modified for correcting deviations of the acquired dimensions from
the tolerance, and causing the modified cutting tool to machine the
workpiece to bring the dimensions of the semi-finished tooth
pattern within the tolerance; and causing the workpiece to be
machined to the full depth to provide the desired tooth
pattern.
2. The method of claim 1, wherein causing the geometry of the
cutting tool to be modified comprises adjusting a machining program
of the numerical control machine and subjecting the cutting tool to
a dressing operation in accordance with the adjusted machining
program, thereby obtaining the modified cutting tool, the dressing
operation performed by a dressing tool configured to create the
geometry in accordance with the adjusted machining program.
3. The method of claim 2, wherein acquiring the dimensions
comprises probing the workpiece at a plurality of locations of the
semi-finished pattern and computing a tooth depth, a tooth width,
and a pressure angle for the semi-finished tooth pattern.
4. The method of claim 3, wherein causing the geometry of the
cutting tool to be modified comprises adjusting the machining
program for causing the pressure angle for the modified cutting
tool to be brought within the tolerance, thereby bringing the
pressure angle for the semi-finished tooth pattern within the
tolerance upon the workpiece being subjected to further machining
by the modified cutting tool.
5. The method of claim 3, wherein causing the geometry of the
cutting tool to be modified comprises adjusting the machining
program for causing a radial distance between the cutting tool and
the dressing tool to be modified and the geometry of the cutting
tool to be shifted radially accordingly for adjusting a radial
offset of the semi-finished tooth pattern, and accordingly bringing
the tooth width for the semi-finished tooth pattern within the
tolerance, upon the workpiece being subjected to further machining
by the modified cutting tool.
6. The method of claim 1, wherein acquiring the dimensions
comprises probing one of an upper and a lower face of the
semi-finished pattern relative to a reference datum and computing a
pitch plane height for the semi-finished tooth pattern, and wherein
causing the workpiece to be machined to the full depth comprises
computing a distance equal to a difference between the computed
pitch plane height and a nominal pitch plane height and causing the
cutting tool to plunge into the workpiece by the distance.
7. The method of claim 1, wherein the acquired dimensions are
compared to the nominal dimensions obtained from a virtual tooth
pattern.
8. The method of claim 7, wherein the virtual tooth pattern is
obtained by scanning surfaces of a master gauge, the virtual tooth
pattern complementary to the desired tooth pattern.
9. A system for machining from a workpiece a toothed member having
a desired tooth pattern, the workpiece machined using a cutting
tool of a numerically controlled machine, the system comprising: a
memory; a processor; and at least one application stored in the
memory and executable by the processor for causing the cutting tool
to machine the workpiece to a first depth to provide a
semi-finished tooth pattern, the semi-finished tooth pattern
created according to a geometry of the cutting tool, the first
depth less than a full depth of the desired tooth pattern;
acquiring dimensions of the semi-finished tooth pattern; comparing
the acquired dimensions to nominal dimensions of the semi-finished
tooth pattern and determining whether the acquired dimensions are
within a predetermined tolerance of the nominal dimensions; if the
acquired dimensions are not within the predetermined tolerance of
the nominal dimensions, causing the geometry of the cutting tool to
be modified for correcting deviations of the acquired dimensions
from the tolerance, and causing the modified cutting tool to
machine the workpiece to bring the dimensions of the semi-finished
tooth pattern within the tolerance; and causing the workpiece to be
machined to the full depth to provide the desired tooth
pattern.
10. The system of claim 9, wherein the at least one application is
executable by the processor for adjusting a machining program of
the numerical control machine and subjecting the cutting tool to a
dressing operation in accordance with the adjusted machining
program, thereby causing the geometry of the cutting tool to be
modified, the dressing operation performed by a dressing tool
configured to create the geometry in accordance with the adjusted
machining program.
11. The system of claim 10, wherein the at least one application is
executable by the processor for probing the workpiece at a
plurality of locations of the semi-finished pattern and computing a
tooth depth, a tooth width, and a pressure angle for the
semi-finished tooth pattern to acquire the dimensions.
12. The system of claim 11, wherein the at least one application is
executable by the processor for adjusting the machining program for
causing the pressure angle for the modified cutting tool to be
brought within the tolerance, thereby bringing the pressure angle
for the semi-finished tooth pattern within the tolerance upon the
workpiece being subjected to further machining by the modified
cutting tool.
13. The system of claim 11, wherein the at least one application is
executable by the processor for adjusting the machining program for
causing a radial distance between the cutting tool and the dressing
tool to be modified and the geometry of the cutting tool to be
shifted radially accordingly for adjusting a radial offset of the
semi-finished tooth pattern, and accordingly bringing the tooth
width for the semi-finished tooth pattern within the tolerance,
upon the workpiece being subjected to further machining by the
modified cutting tool.
14. The system of claim 9, wherein the at least one application is
executable by the processor for probing one of an upper and a lower
face of the semi-finished pattern relative to a reference datum,
computing a pitch plane height for the semi-finished tooth pattern,
computing a distance equal to a difference between the computed
pitch plane height and a nominal pitch plane height, and causing
the cutting tool to plunge into the workpiece by the distance,
thereby causing the workpiece to be machined to the full depth.
15. The system of claim 9, wherein the at least one application is
executable by the processor for acquiring the nominal dimensions by
scanning surfaces of a master gauge to obtain a virtual tooth
pattern complementary to the desired tooth pattern.
16. The system of claim 9, wherein the at least one application is
executable by the processor for causing the workpiece to be
machined to the full depth for achieving the desired tooth pattern
of a curvic coupling.
17. A system for machining from a workpiece a toothed member having
a desired tooth pattern, the workpiece machined using a cutting
tool of a numerically controlled machine, the system comprising:
means for causing the cutting tool to machine the workpiece to a
first depth to provide a semi-finished tooth pattern, the
semi-finished tooth pattern created according to a geometry of the
cutting tool, the first depth less than a full depth up of the
desired tooth pattern; means for acquiring dimensions of the
semi-finished tooth pattern; means for comparing the acquired
dimensions to nominal dimensions of the semi-finished tooth pattern
and determining whether the acquired dimensions are within a
predetermined tolerance of the nominal dimensions; if the acquired
dimensions are not within the predetermined tolerance of the
nominal dimensions, means for causing the geometry of the cutting
tool to be modified for correcting deviations of the acquired
dimensions from the tolerance, and causing the modified cutting
tool to machine the workpiece to bring the dimensions of the
semi-finished tooth pattern within the tolerance; and means for
causing the workpiece to be machined to the full depth to provide
the desired tooth pattern.
Description
TECHNICAL FIELD
[0001] The application relates generally to automated machining of
parts and, more particularly, toothed members.
BACKGROUND OF THE ART
[0002] Toothed members, such as curvic couplings, are commonly
found in gas turbine engines as they provide connection between
engine parts and permit highly precise centering and stacking of
engine parts. Given the tight tolerances required for aerospace
applications, such toothed members have to be machined with great
accuracy in order to ensure proper functioning in the engine.
Therefore, machine tool operators are typically required to make
several manual interventions during the machining process in order
to ensure that parameters (e.g. concentricity, perpendicularity,
addendum, pitch plane height, contact pattern) associated with a
freshly machined toothed member are within required specifications.
In particular, as part of the conventional manufacturing process,
an operator is typically required to use a master gauge, depth
micrometer, and height gauge at various stages of the machining
process to ensure that the dimensions of the freshly machined part
are within tolerance. Given the complexity of the manufacturing
process, a substantial amount of manual measurement and setup
operations is required, which proves time consuming and costly.
[0003] There is therefore a need for improved systems and methods
for manufacturing parts, such as toothed members, that are subject
to tight tolerances.
SUMMARY
[0004] In one aspect, there is provided a computer-implemented
method for machining from a workpiece a toothed member having a
desired tooth pattern, the workpiece machined using a cutting tool
of a numerically controlled machine. The method comprises causing
the cutting tool to machine the workpiece to a first depth to
provide a semi-finished tooth pattern, the semi-finished tooth
pattern created according to a geometry of the cutting tool, the
first depth less than a full depth of the desired tooth pattern,
acquiring dimensions of the semi-finished tooth pattern, comparing
the acquired dimensions to nominal dimensions of the semi-finished
tooth pattern and determining whether the acquired dimensions are
within a predetermined tolerance of the nominal dimensions, if the
acquired dimensions are not within the predetermined tolerance of
the nominal dimensions, causing the geometry of the cutting tool to
be modified for correcting deviations of the acquired dimensions
from the tolerance, and causing the modified cutting tool to
machine the workpiece to bring the dimensions of the semi-finished
tooth pattern within the tolerance, and causing the workpiece to be
machined to the full depth to provide the desired tooth
pattern.
[0005] In another aspect, there is provided a system for machining
from a workpiece a toothed member having a desired tooth pattern,
the workpiece machined using a cutting tool of a numerically
controlled machine. The system comprises a memory, a processor, and
at least one application stored in the memory and executable by the
processor for causing the cutting tool to machine the workpiece to
a first depth to provide a semi-finished tooth pattern, the
semi-finished tooth pattern created according to a geometry of the
cutting tool, the first depth less than a full depth of the desired
tooth pattern, acquiring dimensions of the semi-finished tooth
pattern, comparing the acquired dimensions to nominal dimensions of
the semi-finished tooth pattern and determining whether the
acquired dimensions are within a predetermined tolerance of the
nominal dimensions, if the acquired dimensions are not within the
predetermined tolerance of the nominal dimensions, causing the
geometry of the cutting tool to be modified for correcting
deviations of the acquired dimensions from the tolerance, and
causing the modified cutting tool to machine the workpiece to bring
the dimensions of the semi-finished tooth pattern within the
tolerance, and causing the workpiece to be machined to the full
depth to provide the desired tooth pattern.
[0006] In a further aspect, there is provided a system for
machining from a workpiece a toothed member having a desired tooth
pattern, the workpiece machined using a cutting tool of a
numerically controlled machine. The system comprises means for
causing the cutting tool to machine the workpiece to a first depth
to provide a semi-finished tooth pattern, the semi-finished tooth
pattern created according to a geometry of the cutting tool, the
first depth less than a full depth of the desired tooth pattern,
means for acquiring dimensions of the semi-finished tooth pattern,
means for comparing the acquired dimensions to nominal dimensions
of the semi-finished tooth pattern and determining whether the
acquired dimensions are within a predetermined tolerance of the
nominal dimensions, if the acquired dimensions are not within the
predetermined tolerance of the nominal dimensions, means for
causing the geometry of the cutting tool to be modified for
correcting deviations of the acquired dimensions from the
tolerance, and causing the modified cutting tool to machine the
workpiece to bring the dimensions of the semi-finished tooth
pattern within the tolerance, and means for causing the workpiece
to be machined to the full depth to provide the desired tooth
pattern.
DESCRIPTION OF THE DRAWINGS
[0007] Reference is now made to the accompanying figures in
which:
[0008] FIG. 1 is a schematic cross-sectional view of a gas turbine
engine;
[0009] FIG. 2 is a flowchart of a method for manufacturing a
toothed member, in accordance with an illustrative embodiment;
[0010] FIG. 3 is a flowchart of the step of FIG. 2 of probing and
adjusting a workpiece and fixture setup;
[0011] FIG. 4 is a flowchart of the step of FIG. 2 of adjusting
cutting tool parameters and subjecting the cutting tool to an
initial dressing operation;
[0012] FIG. 5 is a flowchart of the step of FIG. 2 of automated
machining of the workpiece;
[0013] FIG. 6a is a perspective view of a cutting tool machining a
workpiece, in accordance with an illustrative embodiment;
[0014] FIG. 6b is a perspective view of the workpiece of FIG. 6a
being machined to form a toothed member;
[0015] FIG. 6c is a schematic diagram showing the tooth form of a
toothed member, in accordance with an illustrative embodiment;
[0016] FIG. 6d is a schematic diagram showing the profile of a
convex cutting tool, in accordance with an illustrative
embodiment;
[0017] FIG. 6e is a schematic diagram showing the profile of a
concave cutting tool, in accordance with an illustrative
embodiment;
[0018] FIG. 7 is a flowchart of the step of FIG. 5 of correlating
parameters computed for a semi-finished workpiece to master gauge
parameters;
[0019] FIG. 8 illustrates a master gauge under analysis on a
scanning coordinate measuring machine (CMM) and reconstructed
surfaces of the master gauge teeth from the CMM inspection, in
accordance with one embodiment;
[0020] FIG. 9 is a schematic diagram showing dressing of a cutting
tool, in accordance with one embodiment;
[0021] FIG. 10a and FIG. 10b are schematic diagrams showing
redressing of a convex cutting tool profile, in accordance with one
embodiment;
[0022] FIG. 10c and FIG. 10d are schematic diagrams showing
redressing of a concave cutting tool profile, in accordance with
one embodiment;
[0023] FIG. 11 is a flowchart of the step of FIG. 5 of further
machining the semi-finished surface to achieve at the desired
toothed member geometry;
[0024] FIG. 12 is a schematic diagram of a system for machining a
toothed member, in accordance with one embodiment; and
[0025] FIG. 13 is a schematic diagram of an application running on
the processor of FIG. 12.
DETAILED DESCRIPTION
[0026] FIG. 1 illustrates a gas turbine engine 10 of a type
preferably provided for use in subsonic flight, generally
comprising in serial flow communication a fan 12 through which
ambient air is propelled, a compressor section 14 for pressurizing
the air, a combustor 16 in which the compressed air is mixed with
fuel and ignited for generating an annular stream of hot combustion
gases, and a turbine section 18 for extracting energy from the
combustion gases. High pressure rotor(s) 20 of the turbine section
18 are drivingly engaged to high pressure rotor(s) 22 of the
compressor section 14 through a high pressure shaft 24. Low
pressure rotor(s) 26 of the turbine section 18 are drivingly
engaged to the fan rotor 12 and to other low pressure rotor(s) (not
shown) of the compressor section 14 through a low pressure shaft 28
extending within the high pressure shaft 24 and rotating
independently therefrom.
[0027] The engine 10 illustratively comprises various parts, such
as toothed members, that are to be machined with tight tolerances.
The parts may be machined using multi-axis Numerical Control (NC)
(e.g. Computer Numerical Control (CNC)) machining centers. A
cutting tool provided on the NC machine may be used to perform the
machining operation. In one embodiment, the machining operation
comprises a grinding process, e.g. plunge grinding, and the cutting
tool is a grinding wheel (e.g. cup-shaped). Still, it should be
understood that other suitable machining processes and accordingly
other cutting tools, may apply.
[0028] Referring to FIG. 2, a method 100 for manufacturing a
toothed member will now be described. In one embodiment, the method
100 is used to manufacture a curvic coupling, i.e. a toothed
connection member that can be used to transmit torque between
rotating elements. Curvic couplings are commonly found in gas
turbine engines, such as the engine 10 of FIG. 1, for several
reasons. First, curvic couplings can be machined directly onto
rotors such as axial and centrifugal compressors and turbine disks,
eliminating the need for separate shafts. Rotors can then be
stacked closely and accurately with minimal distance between mating
parts. Second, curvic couplings permit highly precise centering of
parts during disassembly and installation in an engine. In
addition, curvic couplings are relatively quick to manufacture if a
suitable machine and cutting tool are available. It should however
be understood that, although the proposed system and method are
presented herein as being used to manufacture curvic couplings,
other toothed members, including, but not limited to, splines,
gears (e.g. bevel gears and spur gears), couplings and slots, may
apply.
[0029] A curvic coupling typically has teeth spaced
circumferentially about its face, the teeth having a curved shape
when viewed in a plane perpendicular to a central (or "coupling")
axis of the curvic coupling and the two opposed sides of a given
tooth in a curvic coupling being curved in opposite directions. Two
mating curvic couplings are typically coupled to create a
connection, with one curvic coupling being made with convex, or
"barrel-shaped", teeth while its mate is made with concave, or
"hour-glass-shaped", teeth. Curvic coupling teeth can be produced
with a wide range of pressure angles to suit various applications.
All teeth of a given curvic coupling are generally ground to a
constant depth and a theoretical radius, which have to be accurate
within prescribed tolerances in order to ensure proper engagement
with mating curvic couplings.
[0030] The method 100 illustratively comprises installing at step
102 into a fixture, e.g. a fixture with a zero-point clamping
system, a workpiece (e.g. an annular-shaped workpiece) to be
machined to obtain a desired toothed member (e.g. curvic coupling
or gear). It is desirable for locating face(s) on the workpiece and
fixture to be manufactured such that tolerances on flatness for the
workpiece and fixture are significantly below those of the finished
toothed member obtained post-machining. The next step 104 is then
to load the workpiece and fixture assembly into an NC machine (e.g.
an NC grinding machine). This may be achieved using an automated
loading/unloading system, such as a robot with a quick change
zero-point clamping system. Alternatively, loading may be performed
by an operator. In one embodiment, once the fixture is placed into
a loading position on a work table of the NC machine, a signal will
be sent by the NC machine to cause clamping or unclamping of the
fixture into position on the work table.
[0031] The setup obtained at step 104 may then be probed and
adjusted as needed at step 106. Referring to FIG. 3, the step 106
of probing and adjusting the workpiece and fixture setup
illustratively comprises probing at step 202 the initial position
of a circular reference datum to verify the parallelism of the
workpiece with a locating face of the fixture. As used herein, the
term "datum" refers to one or more reference points or surface(s)
that measurements are taken from. The circular reference datum may
have been predetermined and defined on the engineering drawings or
manufacturing operation sheet. In one embodiment, the datum used
for measuring parallelism is the face on the workpiece where the
toothed member is ground. However, it should be understood that the
datum could also be two or more diameter locations near the area of
the annular-shaped toothed member. The probing may be performed at
step 202 using a part probing system (e.g. a scanning or touch
probing system) provided on (e.g. integrated with) the NC machine.
In order to acquire measurements, a tip of a probe may be moved
along a pre-programmed (e.g. NC programmed) probing direction
toward positions on the workpiece where measurements are to be
acquired. The probe may further be coupled to a force sensor (not
shown), which acquires a measurement signal when the probe tip
touches the surface of the workpiece. In one embodiment, the
probing system is a strain-gage. It should be understood that other
probing systems or measuring devices may apply. For example, a
coordinate measuring machine (CMM) connected to the NC machining
center may be used to acquire measurements on a surface of the
workpiece.
[0032] A measure of the parallelism of the workpiece relative to
the fixture may be obtained from the acquired measurements. This
may be achieved by probing several points on the face of the
workpiece where the toothed member is ground and computing the
difference between the minimum and maximum height values (e.g.
z-values). Alternatively, a plane may be fitted through a number of
(e.g. three (3)) probed points and the height difference at the
extremes of the plane (at the diameters of the toothed member area)
may then be computed. Multiple points may also be probed and a
plane calculated by a least-squares or regression plane fitting
algorithm. In other embodiments, the measure of the parallelism may
be obtained by finding the center of two or more diameter
locations, one being at the toothed member face, and fitting a
plane whose normal is a line connecting the two (or more)
diameters. If the workpiece is not parallel with the fixture's
locating face and a deviation is measured, the next step 204 may
then be to assess whether the deviation from parallelism is within
a predetermined tolerance. Tolerances referred to herein are
illustratively defined by engineering drawings or manufacturing
operation sheets. Typical values are between 0.0002 and 0.002
inches. If this is not the case, i.e. the deviation is beyond
tolerance, the next step 206 may be to cause realignment of the
workpiece by generate an alarm accordingly. Alternatively, the
misalignment may be corrected at step 206 by implementing a
controller-based compensation method, provided such an option is
available on the NC machine and the latter has an appropriate
number of axes for implementation of the compensation method. In
one embodiment, at least five (5) axes are used for parallelism
compensation, comprising three (3) linear axes and two (2) rotary
axes. The method may then flow back to repeat steps 202 and
204.
[0033] When it is determined at step 204 that the deviation from
parallelism is within tolerance, concentricity of the workpiece
relative to a rotary axis of the NC machine's work table may then
be checked. For this purpose, a series of points may be probed on
the workpiece datum and a circle fitted through the points at step
208. A face is illustratively used as a datum to measure
parallelism, as discussed above, while a diameter is used as a
datum to measure concentricity. However, it should be understood
that it is possible to use two (2) or more diameters (e.g. a
cylinder) as a datum for the parallelism measurement with one of
these diameters being coincident with the same diameter used to
measure concentricity. The more points probed at step 208, the
higher the degree of accuracy. The workpiece will be found to be
concentric with the rotary axis of the NC machine's work table if
the rotary axis passes through the center of the circle fitted
through the probed points. If the workpiece is not concentric with
the work table, it may be assessed at step 210 whether the
deviation from concentricity is within a predetermined tolerance.
Typical tolerances for concentricity of toothed members (e.g.
curvic couplings) are between 0.0002 and 0.002 inches. If this is
not the case, the location of the center of the fitted circle is
shifted as needed at step 212 to bring the concentricity within
tolerance. In one embodiment, only two (2) linear axes (typically X
and Y axes) are needed to compensate for an out-of-concentricity
condition. Such shifting may be performed manually, using a robot,
or by a controller-based compensation method if available. The
method may then flow back to repeat steps 208 and 210. When it is
determined at step 210 that the concentricity is within tolerance,
the method proceeds with the step 108 of FIG. 2 of adjusting the
cutting tool parameters as needed and subjecting the cutting tool
to an initial dressing operation.
[0034] It should be understood that the concentricity may be
verified prior to verifying the parallelism of the workpiece and
the order of steps 202 to 212 may be changed accordingly. It should
also be understood that steps 204 and 210 may not be performed if
it is already determined from the acquired measurements (e.g. at
steps 202 and 208) that no deviation from parallelism or
concentricity exists.
[0035] Referring now to FIG. 4 in addition to FIG. 2, the step 108
of adjusting the cutting tool parameters as needed and subjecting
the cutting tool to an initial dressing operation illustratively
comprises calling the cutting tool to the NC machine's spindle
(e.g. the NC machine's main shaft) from an automatic tool changing
(ATC) system on the NC machine. In some embodiments, the NC machine
may indeed store a plurality of tools in a tool magazine, with each
tool being called (e.g. brought) to the spindle (e.g. by the ATC)
when the tool is to be used. Some NC machines further have
automatic nozzle changing capability, with each cutting tool having
a dedicated coolant manifold to optimally cool and flush the
grinding zone. This eliminates the need for an operator to install
and align nozzles in the setup. The next step 304 may then be to
probe the cutting tool with a suitable measuring device (e.g. laser
or touch tool probing system) to obtain an estimate of the true (or
real) diameter and axial thickness of the cutting tool. The
estimated diameter and axial thickness may then be compared to
nominal dimensions and it may be determined at step 308 whether
offsets (i.e. radial and/or axial) from the nominal dimensions
exist. It may be desirable for the cutting tool to be wide enough
to cover at least half of the width of a space between two adjacent
teeth formed on the workpiece, yet narrow enough to pass through
the tooth space (or tooth slot) during machining.
[0036] As used herein, the term "nominal" as applied to a part,
surface, geometrical element, etc., is intended to refer to the
part, surface, geometrical element (e.g. a surface, profile, angle,
plate, or other feature defining the part), etc., as defined in a
theoretical model such as a Computer Aided Design (CAD) model or
other digitally stored or recreated model, without tolerance, which
may be used as a reference when machining one or a plurality of
similar actual parts, surfaces, geometrical elements, etc. The term
"real", "actual", or "true" as applied to a part, surface,
geometrical element, etc., is intended to refer to the real,
physical part, surface, geometrical element, etc., at various
stages of the manufacturing process, including any variation
brought by that process.
[0037] If it is determined at step 308 that radial and/or axial
offsets from nominal dimensions exist, the one or more offsets are
sent at step 310 to the NC machine controller to cause adjustment
of the cutting tool's thickness and diameter compensation in an NC
dressing program for the cutting tool. If it was determined at step
308 that no offsets exist or after step 310 has been performed, the
cutting tool is subjected at step 312 to an initial dressing
operation in accordance with the NC dressing program.
[0038] In one embodiment, the cutting tool is a dressable
cup-shaped grinding wheel that may be dressed by the use of a
dressing tool, such as a wheel or grinding dresser. In one
embodiment, the dressing tool is a rotary dresser, e.g. a disc with
a hard material, such as diamond, attached to the edge. It should
however be understood that other types of dressing tools, e.g.
stationary dressing tools, may apply. It should also be understood
that, although toothed members, such as curvic couplings, may be
ground using plated grinding wheels, where the tooth form is
manufactured onto the wheel, it is preferable to use dressable
wheels to ensure on-machine adjustment of the shape of the toothed
member, as will be discussed further below. As used herein, the
term dressing refers to an operation of removing a current layer of
abrasive material on the cutting tool so as to modify a profile of
the cutting tool. The abrasive material includes, but is not
limited to, aluminum oxide, silicon carbide, and vitrified cubic
boron nitride (CBN), with each abrasive grain serving as a small
cutting element. Selection of the abrasive material illustratively
depends on cost, required tolerances, and part material.
[0039] The NC dressing program is illustratively generated to move
the face of the cutting tool (e.g. the grinding wheel) across the
radius (or edge) of the dressing tool in order to create a desired
profile for the cutting tool, the profile corresponding to a shape
required by the dimensions of the toothed member to be machined.
Indeed, the dressing operation performed at step 312 in accordance
with the NC dressing program illustratively modifies the profile
(or geometry) of the cutting tool so as to achieve in the cutting
tool a profile that will create a desired tooth profile or pattern
(e.g. as defined in a theoretical model such as a CAD model) in the
toothed member when the latter is machined by the cutting tool. The
dressing operation of step 312 may involve plunging the cutting
tool, e.g. the grinding wheel, into a shaped roll of abrasive
material. Alternatively, the required shape may be formed on the
grinding wheel by moving the latter over a radius on a single point
or rotary-type dresser in accordance with the NC dressing program.
The latter technique may be preferable as it allows for the tooth
profile to be modified by adjusting the NC program for correcting
errors owing to stackup of tolerances or misalignments in axes of
the NC machine cutting tool. In one embodiment, an acoustic
emission sensor may be employed to find the position where the
cutting tool touches the dresser and to ensure an even and complete
dressing of the cutting tool. The NC dressing program may be fully
parametric, e.g. equation-based, such that the dressing tool path
and hence the shape of the cutting tool (e.g. the wheel shape) can
be updated by changing parameters in the NC program from the probed
dimensions (i.e. pressure angle and tooth width).
[0040] Referring back to FIG. 2, after the cutting tool has been
initially dressed at step 108, automated machining of the workpiece
may be performed at step 110, as will be discussed further below
with reference to FIG. 5. Step 110 illustratively comprises
generating a machining (e.g. NC) program comprising commands that
indicate a numerically-controlled tool path to be followed by at
least the cutting tool for machining the workpiece and
manufacturing the toothed member. Similarly to the NC dressing
program, the NC machining (e.g. grinding) program may be fully
parametric, e.g. equation-based, such that the machining tool path
is updated by changing parameters in the NC program.
Post-machining, the machined workpiece (i.e. the finished toothed
member) may be inspected at step 112. Step 112 may comprise
verifying concentricity, perpendicularity, and/or parallelism of
the freshly machined workpiece by probing. For this purpose, the
automated loading/unloading system (or the operator) removes the
workpiece and fixture from the NC machine and the workpiece is sent
to an inspection station at a remote location. In one embodiment,
three (3) or more teeth are probed on the machined workpiece to
measure concentricity, perpendicularity, and parallelism of the
tooth pattern. A contact pattern check typical for inspection of
toothed members, such as curvic coupling, may also be performed on
the machined workpiece. In one embodiment, the contact pattern
check may comprise application of a gear marking compound on a
master gauge, which may be a produced toothed member having a
geometry that is complementary (e.g. the mirror image) to that of
the toothed member to be machined. The master gauge is then seated
on the freshly machined workpiece, tapped into place using a
suitable tool (e.g. a hammer) and removed. The gear compound
transferred to the teeth on the workpiece then indicates the manner
in which the mating teeth (i.e. the teeth of the master gauge and
of the machined workpiece) contact each other. From the transfer
pattern of the gear compound, it can be determined if satisfactory
contact is made between the master gauge and the freshly machined
workpiece. An acceptable contact pattern may be defined by
requirements such as a well-centered shape, a given percentage of
teeth in contact, and a limited number of consecutive teeth missing
contact.
[0041] In the proposed automated machining process, an acceptable
contact pattern may be ensured at step 112 by selecting a suitable
abrasive material for the cutting tool. An acceptable contact
pattern can also be ensured by sufficiently dressing the cutting
tool at step 108 to ensure that the cutting tool's form does not
break down during the machining process and that any undesirable
tooth profiles that may be found on the workpiece are completely
removed. In addition, the pressure angle, tooth geometry and
machine offsets may be initially verified on a test ring with the
above-mentioned contact pattern check. Periodic measurements and
adjustments can be taken from time to time to reduce the
possibility of drift. Moreover, using a precise, well-aligned and
well-maintained machine and ensuring the dressing tool is replaced
at suitable intervals to prevent excessive wear to machine the
workpiece can achieve an acceptable contact pattern. Finally,
keeping the NC machine and probing system accurate and well-aligned
through frequent calibrations and adjustments (e.g. ball-bar
checks) can also achieve an acceptable contact pattern.
[0042] If the contact pattern is found to be unacceptable at step
112, the NC machine and NC program may be recalibrated and
adjusted. Acceptable results may be confirmed by testing on
representative test rings. The workpiece can then be returned to
the NC machine for a rework cycle (i.e. for repeating steps 102 to
112). Removing a small amount of material by plunging into the
workpiece with a correctly dressed cutting tool will usually be
sufficient to restore the workpiece surfaces to an acceptable
contact pattern.
[0043] Referring now to FIG. 5, the step 110 of automated machining
of the workpiece illustratively comprises the step 402 of
positioning the cutting tool over the workpiece at a desired
location. At step 404, the workpiece is exposed to the cutting
tool, e.g. the cutting tool is plunged into the workpiece up to a
predetermined partial depth, in order to obtain a semi-finished
surface comprising a plurality of rough tooth slots. The partial
depth is smaller than the desired full depth up to which the
workpiece is to be machined. In one embodiment, the partial depth
is in a range between 30% and 50% of the full depth. It should be
understood that other ranges may apply so long as the partial depth
that is reached enables to measure parameters (e.g. dimensions) of
the semi-finished surface (as will be discussed further below) and
allows for subsequent adjustments (e.g. further machining) to be
performed on the semi-finished surface, if needed.
[0044] The next step 406 may therefore be to assess whether the
predetermined partial depth has been reached. If this is not the
case, the workpiece may be further machined by returning to step
404. Once the cutting tool has machined the workpiece up to the
partial depth as determined at step 406, the next step may be to
retract the cutting tool and assess at step 410 whether more teeth
need to be machined. If this is the case, the rotary axis of the NC
machine's work table may be indexed to the next set of teeth to be
machined and the method may flow back to step 404 for repeating the
machining process for the next set of teeth. The procedure is
repeated until all teeth are ground in the workpiece up to the
required partial depth. It should be understood that, depending on
the requirements, each tooth may be machined up to the partial
depth in several steps. For example, in order to achieve a desired
tooth taper towards the center of the toothed member, the cutting
tool may first machine half of each tooth slot and the workpiece
rotated for machining the other half of the tooth slot. Also, due
to the cutting tool's annular shape and position (e.g. off-axis)
over the workpiece, during each pass of the cutting tool, the half
of a first tooth slot may be machined concurrently to the half of a
second tooth slot located a predetermined distance (e.g. eight (8)
to ten (10) teeth) away from the first tooth slot. In this manner,
teeth can be machined using an event amount of material and balance
can be achieved in the machining process.
[0045] Once it is determined at step 410 that the workpiece has
been machined such that all teeth have been ground up to the
partial depth, the method may flow to the step 412 of probing the
resulting semi-finished surface. The semi-finished surface may be
probed using any suitable measuring device, such as an on-machine
part probing system, scanning probe, touch probe, or the like, as
discussed above and step 412 may therefore comprise instructing the
measuring device to acquire the measurements (e.g. dimensions) of
the workpiece. In one embodiment, locations on a top face and a
bottom surface of the workpiece as well as two or more points on
each pressure surface of one or more teeth of the workpiece are
probed. Parameters (e.g. dimensions) of the machined workpiece may
then be computed on the basis the measurements acquired by probing.
In one embodiment where curvic couplings are being machined, the
tooth depth, tooth width, and pressure angle are computed. It
should be understood that in other embodiments, more or less
parameters may be computed. For example, an "X value" parameter,
which is indicative of a distance from the center of the cutting
tool to the center of the workpiece, may be computed. Also, when
the method described herein is used to manufacture a spline,
different geometry may be measured and calculated. It should also
be understood that other dimensions of the workpiece, including but
not limited to surface finish, temperature, or the like, may be
acquired.
[0046] As will be discussed further below with reference to FIG. 7,
at step 414, the computed parameters may then be compared to
theoretical parameters, e.g. parameters obtained from a virtual
tooth profile, such as a scanned master gauge, the NC program
adjusted, and the cutting tool subjected to further dressing as
needed. If the cutting tool is redressed, the workpiece is
illustratively subjected to further machining by the redressed
cutting tool at step 416 in order to bring the parameters of the
semi-finished surface within tolerance of the theoretical
parameters. After the workpiece is further machined, steps 412 and
414 may be repeated until none of the parameters are found at step
414 to be beyond tolerance. Once it is found that the parameters of
the semi-finished surface are within tolerance of the theoretical
parameters, the semi-finished surface may be further machined at
step 418, i.e. the rough slots machined by the cutting tool up to
the full depth, in order to achieve the desired toothed member
geometry, as will be discussed further below.
[0047] FIG. 6a illustrates a cutting tool, i.e. a grinding wheel
502, being plunged into (e.g. along the direction of arrow A) an
annular workpiece 504 for grinding along a perimeter thereof a
plurality of teeth as in 506. In the illustrated embodiment, the
workpiece is being machined to form a convex curvic coupling. It
can be seen from the embodiment of FIG. 6a that the grinding wheel
502 has an axis of rotation B and is not concentric with the
workpiece 504.
[0048] As can be seen in FIG. 6b, the teeth 506 machined in the
workpiece 504, e.g. the curvic coupling, each have a root 508 and a
pressure surface 510. The tooth depth 512 can be measured as the
overall height of each tooth 506 as measured from the root 508
while the tooth thickness 514 is the width of each tooth at the
addendum (not shown). As can be seen in FIG. 6c, which illustrates
the tooth form for a toothed member, such as the curvic coupling
504 of FIG. 6b, each tooth 506 further has a given pressure angle
516 that is measured as the angle between a tangent to the tooth
profile (i.e. a tangent to the pressure surface 510) and a line
perpendicular to the pitch plane (or pitch surface) 518. Other
geometrical elements of the teeth 506 (e.g. the dedendum, addendum,
gable, and the like) will be apparent to those skilled in the
art.
[0049] Referring to FIG. 6d in addition to FIG. 6a, there is
illustrated a profile (not to scale) of the grinding wheel 502 for
a convex curvic coupling, in accordance with one embodiment. It
should be understood that various profiles other than the one
illustrated in FIG. 6d may apply. The grinding wheel's profile
comprises, at an inner diameter (ID) of the wheel 502 (referred to
"Wheel ID" in FIG. 6d), an inner surface 602, an outer surface 604
at an outer diameter (OD) of the wheel 502 (referred to "Wheel OD"
in FIG. 6d), and a bottom face or edge, referred to as a gable 606.
The gable 606 usually has a small angle .phi..sub.g of zero (0) to
five (5) degrees in order to eliminate the mismatch between the two
sides of a tooth. If the gable angle is zero, a mismatch results
from the fact that for each tooth (e.g. machined using the grinding
wheel 502), one half is ground at one contact arc between the
grinding wheel 502 and the workpiece, while the other is ground at
a second arc. However, for a particular tooth, the two tooth halves
are illustratively not ground simultaneously, as discussed above.
As can be seen from FIG. 6a, the shape root plane (not shown) of
the workpiece 504 can be created by the gable 606 of the grinding
wheel 502 while the pressure surfaces (reference 510 in FIG. 6b)
are shaped by the inner and/or outer surfaces 602, 604 respectively
provided at an inner diameter (ID) and an outer diameter (OD) of
the wheel 502. In particular, the convex tooth profile of the
machined curvic coupling may be produced by the inner surface 602
of the grinding wheel 502 with the pressure surfaces 510 of the
toothed member being created by a pressure surface 608 provided at
the wheel's inner surface 602. The pressure angle .phi..sub.P of
the pressure surface 608 in turn defines the toothed member's
pressure angle (reference 516 in FIG. 6c). Therefore, the profile
of the grinding wheel 502 determines the tooth profile created in
the machined toothed member and the cutting tool is dressed
accordingly to achieve a desired tooth profile.
[0050] FIG. 6e illustrates, in accordance with one embodiment, a
profile of a concave grinding wheel 502' used to machine concave
curvic couplings that match the convex curvic couplings machined
using the grinding wheel 502 of FIG. 6d. The grinding wheel 502'
comprises an inner surface 602' at the ID of the wheel 502'
(referred to "Wheel ID" in FIG. 6e), an outer surface 604' at the
OD of the wheel 502' (referred to "Wheel OD" in FIG. 6e), and a
gable 606' having an angle .phi..sub.g. The pressure surfaces of a
concave toothed member are created by a pressure surface 608'
provided at the wheel's outer surface 604'. The pressure angle
.phi..sub.P of the pressure surface 608' in turn defines the
toothed member's pressure angle (reference 516 in FIG. 6c). The
concave profile of the wheel 502' is illustratively a mirror image
of the convex profile of the wheel 502 of FIG. 6d about an axis C,
which is substantially parallel to the tool axis B and centered at
the wheel's pitch plane points (references 610 and 610' in FIG. 6d
and FIG. 6e).
[0051] Referring now to FIG. 7, the step 414 of comparing the
parameters (e.g. tooth depth, tooth width, and pressure angle)
computed for the partially-machined (i.e. semi-finished) workpiece
to theoretical (or nominal) dimensions illustratively comprises
correlating the computed parameters with theoretical parameters
defined in a theoretical model for the toothed member to be
machined. In one embodiment, the theoretical parameters are
obtained from a master gauge, which has been designed and produced
to have the desired tooth profile to be achieved in the finished
toothed member. It should however be understood that the
theoretical parameters may alternatively be obtained from a solid
model of a nominal part. Still, since machined parts are typically
inspected post-machining using a master gauge, as discussed herein
above, and since mater gauges typically exhibit deviations from
nominal part models, it is preferable to calibrate the probed
toothed member dimensions with respect to the master gauge. Step
414 therefore illustratively comprises characterizing the master
gauge to determine parameters thereof at step 702. This may involve
scanning the master gauge surfaces using a high precision
measurement system. For example, as illustrated in FIG. 8, the
master gauge 802 may be analyzed on a scanning CMM 804.
Reconstructed surfaces 806 of the master gauge teeth may then be
obtained from the CMM inspection and used to compute the master
gauge's dimensions. Alternatively, the master gauge parameters may
be determined at step 702 by installing the master gauge on the
machined workpiece and inferring the master gauge dimensions
through measurement with manual gauging.
[0052] The tooth width and pressure angle computed at step 412 of
FIG. 5 are then compared at step 704 to the theoretical tooth width
and pressure angle values obtained from characterization of the
master gauge. This may be done by computing a difference or
deviation between the computed and theoretical values. Once the
computed pressure angle has been compared to that determined form
the master gauge, the method may assess at step 706 whether the
computed pressure angle is beyond a predetermined tolerance of the
theoretical pressure angle (e.g. obtained from the master gauge
measurements). The tolerance is illustratively defined by
engineering drawings or manufacturing operation sheets. In one
embodiment, the tolerance is .+-.5 minutes of a degree. If this is
not the case (i.e. the computed pressure angle is not beyond a
predetermined tolerance of the theoretical pressure angle), the
method may flow to the step 418 of FIG. 5, i.e. further machine the
semi-finished surface to achieve the desired toothed member
geometry. Otherwise, if the computed pressure angle is beyond the
tolerance, the NC dressing program is accordingly adjusted at step
708 such that, upon the cutting tool being redressed, the cutting
tool's profile (e.g. the inner surface of the cutting tool) has a
corrected pressure angle that in turn brings the pressure angle of
the workpiece machined with the redressed cutting tool within
tolerance. Indeed, since the workpiece's tooth pattern is created
by the cutting tool's geometry and the profile of the cutting tool
accordingly corresponds to the tooth pattern to be achieved, the
workpiece's pressure angle can be adjusted by modifying the cutting
tool's pressure angle.
[0053] At step 708, the cutting tool is thus subjected to a new
dressing operation according to the adjusted NC program, leading to
a redressed cutting tool having a corrected form (i.e. a pressure
angle within tolerance). It should be understood that when
adjusting the pressure angle and redressing the cutting tool
accordingly, it is desirable to ensure that enough material is
removed from the cutting tool so that the previous pressure angle
is completely removed from the cutting tool's profile and replaced
with the new pressure angle. In one embodiment, due to high
sensitivity to pressure angle, the pressure angle need only be
modified slightly (e.g. by less than one (1) degree) in order to
achieve a desired correction. Also, rather than adjusting the
pressure angle by redressing the cutting tool, the pressure angle
may be adjusted by tilting (e.g. angling) the cutting tool relative
to the axis B of FIG. 6d. Still, redressing may be desirable in
order to ensure full automation of the machining process and
minimize human intervention. The next step 416 may then be to
subject the workpiece to further machining using the redressed
cutting tool, as discussed above with reference to FIG. 5. As a
result of redressing the cutting tool, the pressure angle of the
re-machined workpiece is brought within tolerance of the master
gauge pressure angle.
[0054] Once the computed tooth width has been compared to the tooth
width determined form the master gauge, the method may further
assess at step 710 whether the computed tooth width is beyond a
predetermined tolerance of the theoretical (e.g. master gauge)
tooth width. The tolerance is illustratively defined by engineering
drawings or manufacturing operation sheets. In one embodiment, the
tolerance is .+-.0.0006 inches. It should however be understood
that compliance of the tooth width with tolerances may be verified
prior to verifying compliance of the pressure angle with tolerances
and the order of steps 706 to 712 may be changed accordingly. If it
is determined at step 710 that the computed tooth width is within
tolerance, the method may flow to the step 418 of FIG. 5, i.e.
further machine the semi-finished surface to achieve the desired
toothed member geometry. Otherwise, if the computed tooth width is
beyond the tolerance, the radial location of the cutting tool's
profile (i.e. adjusting the radial distance between the cutting
tool and the dressing tool) is automatically modified in the NC
program at step 712. Indeed, since the workpiece's tooth pattern is
created by the cutting tool's geometry and the profile of the
cutting tool accordingly corresponds to the tooth pattern to be
achieved, the workpiece's tooth width can be adjusted by adjusting
the radial location of the cutting tool's profile. The cutting tool
is then subjected to a new dressing operation according to the
modified NC program and the workpiece subjected to further
machining at step 416 using the redressed cutting tool, as
discussed above with reference to FIG. 5. The entire cycle of
probing, comparing, redressing and machining the workpiece with the
redressed cutting tool may then be repeated as necessary until the
workpiece's tooth width is brought within tolerance of the master
gauge tooth width.
[0055] Referring back to FIG. 6c, the tooth width 514 measured on
the workpiece 504 is illustrated. It can be seen from FIG. 6c that
the tooth width 514 can be controlled by adjusting the radial
offset 518, and accordingly by adjusting the radial location of the
cutting tool's profile. Indeed, adjusting the value of the radial
offset 518 modifies the shift or deviation in the radial direction
R(x,y) of the workpiece's tooth profile relative to the nominal
tooth profile. It can be seen from FIG. 9 that, if the radial
offset is sufficiently small (e.g. when 75% of the tolerance of the
engineering drawing or manufacturing operating sheet is achieved),
meaning that the deviation of the measured tooth width from the
nominal tooth width is small (i.e. within tolerance), no redressing
of the cutting tool may be needed.
[0056] As shown in FIG. 9, the radial location of the cutting
tool's profile, e.g. the profile of the grinding wheel 502, can be
adjusted by shifting (e.g. in the X or Y direction) the driving
point 902 of the cutting tool 502 and subsequently redressing the
cutting tool 502. The cutting tool's driving point 902 is
illustratively defined in the NC program as a point where the
cutting tool 502 is controlled by the NC machine. In the
illustrated embodiment, the driving point 902 is located on the
gable (reference 606 in FIG. 6d) of the cutting tool 502. It should
be understood that the driving point 902 may alternatively be
located at another location on the cutting tool 502, as defined by
a user.
[0057] FIG. 9 further illustrates the NC toolpath that the cutting
tool 502 takes for OD and ID dressing, with the convex curvic tooth
form shown. In one embodiment, the dressing tool 904 is fixed and
has a given dressing radius or edge (not shown) and the face of the
cutting tool 502 is moved across the dressing radius in order to
create a desired profile for the cutting tool 502. In the
illustrated embodiment, one side (OD or ID) of the cutting tool 502
is dressed first in a series of passes where the cutting tool 502
travels from an initial (e.g. "Start ID dress" or "Start OD dress")
position to a final (or "End OD and ID dress") position and the
cutting tool 502 is shifted downwards (along the Z axis, in the
direction of arrow F) after each pass. The cutting tool 502 is then
re-positioned to the initial position at the opposite side (OD if
the ID side was dressed first) and the procedure is repeated until
both sides of the cutting tool 502 are fully dressed with the
desired (e.g. new) shape. After a number of successive dressing
passes, the cutting tool 502 is then dressed from an initial tooth
profile 906 (referred to as "Original profile" in FIG. 9) to a
final profile 908 (referred to as "New profile" in FIG. 9). One
side 910 of the dressing tool 904 illustratively dresses the
cutting tool's ID side (e.g. the inner surface 602) while the
opposite side 912 of the dressing tool 904 dresses the cutting
tool's OD side (e.g. the outer surface 604).
[0058] Depending on the required tool width adjustment, the driving
point 902 may be shifted closer to (e.g. in the direction of arrow
D) or further away from (e.g. in the direction of arrow E) the
dressing tool 904, with the latter remaining stationary and
dressing the cutting tool 502 upwards. The cutting tool's profile
can then be shifted accordingly during the dressing cycle, as shown
in FIG. 10a, FIG. 10b, FIG. 10c, and FIG. 10b. FIG. 10a and FIG.
10b illustrate shifting the radial location of a convex tooth
profile while FIG. 10c and Fi. 10d illustrate shifting the radial
location of a concave tooth profile.
[0059] In FIG. 10a, the driving point 902 of the convex cutting
tool 502 is shifted (e.g. offset) towards the outer diameter (OD)
of the cutting tool 502 (i.e. in the direction of arrow E) during
dressing. As a result of the dressing operation performed by the
dressing tool 904, a layer 1002 of abrasive material is removed
from the cutting tool 502 and the cutting tool's profile is
modified from the initial profile 906 (drawn as the bottom solid
line in FIG. 10a) to the final profile 908a (drawn as the top solid
line in FIG. 10a resulting from removal of the abrasive layer
1002). In particular, the profile 906 is shifted radially towards
the inner diameter (ID) of the cutting tool 502 (i.e. in the
direction of arrow 1004a) and shifted upwards (i.e. in the
direction of arrow 1006a) to achieve the profile 908a. It can be
seen that the profile 908a differs from a profile 1007a (drawn
using a dashed line on FIG. 10a) that would have been achieved
after dressing if the radial location of the driving point 902 had
not been offset. Since the cutting tool's profile is shifted
radially towards ID, the tooth width (reference 514 in FIG. 6c)
created in the workpiece (reference 504 in FIG. 6c) with the
grinding wheel 502 redressed in this manner will therefore be
thinner than the tooth width machined using the original (not
redressed) grinding wheel 502.
[0060] In FIG. 10b, the driving point 902 is offset towards ID
(i.e. in the direction of arrow D) and the cutting tool's profile
is therefore shifted radially towards OD (i.e. in the direction of
arrow 1004b) and shifted upwards (i.e. in the direction of arrow
1006b) to achieve the final profile 908b (drawn as the upper solid
profile line in FIG. 10b). As a result, the tooth width 514 will be
wider. It can be seen that the profile 908b differs from a profile
1007b (drawn using a dashed line on FIG. 10b) that would have been
achieved after dressing if the radial location of the driving point
902 had not been offset.
[0061] In FIG. 10c, the driving point 902' of a concave cutting
tool 502' is offset towards OD (i.e. in the direction of arrow E)
and the cutting tool's profile is accordingly modified from the
initial profile 906' (drawn as the bottom solid profile line in
FIG. 10c) to the final profile 908c (drawn as the upper solid
profile line in FIG. 10c), with the profile 906' being shifted
radially towards OD (i.e. in the direction of arrow 1004c) and
shifted upwards (i.e. in the direction of arrow 1006c) to achieve
the profile 908c. As a result, the tooth width 514 will be thinner.
It can be seen that the profile 908c differs from a profile 1007c
(drawn using a dashed line on FIG. 10c) that would have been
achieved after dressing if the radial location of the driving point
902' had not been offset.
[0062] In FIG. 10d, the driving point 902' is offset towards ID
(i.e. in the direction of arrow D) and the cutting tool's profile
is shifted radially towards ID (i.e. in the direction of arrow
1004d) and shifted upwards (i.e. in the direction of arrow 1006d)
to achieve the final profile 908d (drawn as the upper solid profile
line in FIG. 10d). As a result, the tooth width 514 will be wider.
It can be seen that the profile 908d differs from a profile 1007d
(drawn using a dashed line on FIG. 10d) that would have been
achieved after dressing if the radial location of the driving point
902' had not been offset.
[0063] Referring now to FIG. 11 and FIG. 6c, the step 418 of
further machining the semi-finished surface to achieve the desired
toothed member geometry illustratively comprises generating a
machining program for bringing the height (reference 520 in FIG.
6c) of the workpiece's pitch plane (reference 516 in FIG. 6c) to a
nominal pitch plane height (e.g. determined from the master gauge).
In order to determine the pitch plane height 520, the semi-finished
surface, particularly the top and/or bottom face of the machined
workpiece, is probed at step 1102 versus a reference datum
(reference 522 in FIG. 6c) that may be defined on the workpiece or
fixture. Knowing the value of the tooth depth measured on the
semi-finished workpiece (at step 412 in FIG. 5), the pitch height
520 can be calculated on the basis of the acquired measurements. A
difference between the computed pitch plane height 520 and the
nominal pitch plane height is then computed at step 1104. At step
1106, it is determined from the computed difference a distance (in
the Z or "plunge" direction of FIG. 6c) by which to further machine
the workpiece until the pitch plane height is brought to nominal.
At step 1108, the cutting tool is then plunged into the workpiece
by the distance determined at step 1106, thereby bringing the pitch
plane height to nominal and achieving the desired finished surface
(i.e. the desired toothed member geometry).
[0064] Referring now to FIG. 12, a system 1200 for machining a
toothed member will now be described. The system 1200 comprises one
or more server(s) 1202. For example, a series of servers
corresponding to a web server, an application server, and a
database server may be used. These servers are all represented by
server 1202 in FIG. 12. The server 1202 is in communication over a
network 1204, such as the Internet, a cellular network, or others
known to those skilled in the art, with a Computer Numerical
Control (CNC) machining center 1206. The CNC machining center 1206
may comprise a CNC machine 1208 comprising a cutting tool (not
shown) adapted to machine a workpiece (not shown) into the desired
toothed member. The cutting tool part of the CNC machine 1208 may
be dressed using a dressing tool 1210. The CNC machining center
1206 may further comprise a measuring device 1212, such as a
probing system (not shown) integrated with the CNC machine 1208 or
a CMM (not shown). It should be understood that the measuring
device 1212 may comprise any other suitable part sensing system
using one of a variety of contact and non-contact technologies.
[0065] The server 1202 may comprise, amongst other things, a
processor 1214 coupled to a memory 1216 and having a plurality of
applications 1218a, . . . , 1218n running thereon. The processor
1214 may access the memory 1316 to retrieve data. The processor
1214 may be any device that can perform operations on data.
Examples are a central processing unit (CPU), a microprocessor, and
a front-end processor. The applications 1218a, . . . , 1218n are
coupled to the processor 1214 and configured to perform various
tasks as explained below in more detail. It should be understood
that while the applications 1218a, . . . , 12318n presented herein
are illustrated and described as separate entities, they may be
combined or separated in a variety of ways.
[0066] The memory 1216 accessible by the processor 1214 may receive
and store data. The memory 1216 may be a main memory, such as a
high speed Random Access Memory (RAM), or an auxiliary storage
unit, such as a hard disk or flash memory. The memory 1216 may be
any other type of memory, such as a Read-Only Memory (ROM),
Erasable Programmable Read-Only Memory (EPROM), or optical storage
media such as a videodisc and a compact disc.
[0067] One or more databases 1220 may be integrated directly into
the memory 1216 or may be provided separately therefrom and
remotely from the server 1202 (as illustrated). In the case of a
remote access to the databases 1220, access may occur via any type
of network 1204, as indicated above. The databases 1220 described
herein may be provided as collections of data or information
organized for rapid search and retrieval by a computer. The
databases 1220 may be structured to facilitate storage, retrieval,
modification, and deletion of data in conjunction with various
data-processing operations. The databases 1220 may consist of a
file or sets of files that can be broken down into records, each of
which consists of one or more fields. Database information may be
retrieved through queries using keywords and sorting commands, in
order to rapidly search, rearrange, group, and select the field.
The databases 1220 may be any organization of data on a data
storage medium, such as one or more servers.
[0068] In one embodiment, the databases 1220 are secure web servers
and Hypertext Transport Protocol Secure (HTTPS) capable of
supporting Transport Layer Security (TLS), which is a protocol used
for access to the data. Communications to and from the secure web
servers may be secured using Secure Sockets Layer (SSL). Identity
verification of a user may be performed using usernames and
passwords for all users. Various levels of access rights may be
provided to multiple levels of users.
[0069] Alternatively, any known communication protocols that enable
devices within a computer network to exchange information may be
used. Examples of protocols are as follows: IP (Internet Protocol),
UDP (User Datagram Protocol), TCP (Transmission Control Protocol),
DHCP (Dynamic Host Configuration Protocol), HTTP (Hypertext
Transfer Protocol), FTP (File Transfer Protocol), Telnet (Telnet
Remote Protocol), SSH (Secure Shell Remote Protocol).
[0070] FIG. 13 is an exemplary embodiment of an application 1218a
running on the processor 1214. The application 1218a illustratively
comprises a receiving module 1302, a probing and comparison module
1304, a cutting tool redressing module 1306, a machining program
module 1308, and an output module 1310, used to implement the
methods described herein above with reference to FIGS. 2 to 5, FIG.
7, and FIG. 11.
[0071] The receiving module 1302 illustratively receives a signal
indicating that a workpiece to be machined is in a loading position
on the NC machine 1208. The machining program module 1308 then
generates a control signal (e.g. NC program) comprising
instructions to cause the cutting tool to plunge into the workpiece
up to a predetermined partial depth. The control signal may be sent
by the output module 1310 to the cutting tool provided on the NC
machine 1208. Once the semi-finished surface has been obtained, the
probing and comparison module 1304 may then output (e.g. via the
output module 1310) a control signal comprising instructions to
cause the measuring device (reference 1212 of FIG. 13) to acquire
measurements (e.g. dimensions) of the semi-finished surface. The
measurements may then be received at the receiving module 1302 and
compared at the probing and comparison module 1304 to nominal
dimensions, which may be retrieved from the memory 1216 and/or
databases 1220. If the probing and comparison module 1304
determines that the measurements are not within tolerance of the
nominal measurements (or dimensions), the cutting tool redressing
module 1306 may be used for generating and outputting to the
dressing tool (reference 1210 in FIG. 12) a control signal
comprising instructions to cause redressing of the cutting tool in
order to bring the measurements within tolerance. After the cutting
tool has been redressed, the machining program module 1308 may
generate a signal for causing further machining of the workpiece
using the redressed cutting tool. New measurements may then be
acquired, as instructed by the probing and comparison module 1304,
and correlated to nominal measurements. Once the probing and
comparison module 1304 determines that the measurements are within
tolerance of the nominal dimensions, the machining program module
1308 may then be used for generating and outputting to the cutting
tool a control signal (e.g. NC program) comprising instructions to
cause further machining of the workpiece in order to achieve the
finished toothed member.
[0072] It should be understood that, although the method 100 and
system 1200 have been described above with reference to a curvic
coupling, other toothed members may apply, as discussed above.
Also, it should be understood that the method 100 and system 1200
may apply to other types of engines than the one illustrated in
FIG. 1. As discussed above, it should further be understood that
the method 100 and system 1200 may apply to any suitable
manufacturing process. Using the method 100 and system 1200,
toothed members can be machined automatically and precisely on a
machine tool with little to no intervention from an operator.
Automating the process in turn reduces the time required to
manufacture the parts, reduces manufacturing costs, and increases
manufacturing quality and repeatability.
[0073] The above description is meant to be exemplary only, and one
skilled in the art will recognize that changes may be made to the
embodiments described without departing from the scope of the
invention disclosed. Modifications which fall within the scope of
the present invention will be apparent to those skilled in the art,
in light of a review of this disclosure, and such modifications are
intended to fall within the appended claims.
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